Method of finishing gear tooth surfaces



y 1943- H. FALK 2,325,237

METHOD OF FINISHING GEAR TOOTH SURFACES Original Filed 001:. 9, 1956 v2Sheets-Sheet 1 INVENTOR- ATTORNEY.

July 27, 1943.

Original Filed 001:. 9, 1936 HMMF ets-Sheet 2 INVENTOR.

ATTORNEY.

Patented July 27, 1943 METHOD OF FINISHING GEAR TOOTH SURFACES Herman W.Falk, Milwaukee, 'Wis., assignor to Falk Corporation, Milwaukee, Wis., acorporation of Wisconsin Continuation of application Serial No. 104,854,October 9, 1936. This application April 8, 1939,

Serial No. 266,870

1 Claim.

This application relates to a method for finishing gear tooth surfacesand constitutes a continuation of my application Serial No. 104,854,filed October 9, 1936. The method consists in subjecting a fractionalpart of the length of a gear tooth face to finishing stresses andsuccessively shifting the zone of said stress over the working surfaceof the gear. It is thus possible to apply finishing stresses of highunit intensity without dangerous overload of the gear so that burnishingmay be rapidly accomplished, or, if it is desired, it is thus possibleto apply finishing stresses in conjunction with a fine abrasive to bringabout lapping or selective lapping of those areas projecting beyond aselected contour.

The method of'this invention makes possible the formation of glazed orburnished finishes on tooth faces in short intervals of time and withthe expenditure of very little power. This invention also involves amethod of selective lapping of gear teeth in contrast to the generallapping heretofore known, making possible a final correction of toothcontour heretofore unattainable. For the above reasons the'applicationof the method of this invention is useful in the treatment of gears ofany size from the gears of precision instruments, such as watches, togears of the largest size.

In obtaining lapping and burnishing, according to this invention, thegear being treated may be, for example, caused to rotate and to drive anintermeshing, resisting pinion. The resisting pinionis drivingly coupledwith the rotating gear so that a driving reaction resulting from theresisting action and equal thereto is communicated to some point ofreference on the gear to be treated, in a regenerative manner. Thispoint of reference may be a fixed point on the gear being treated, ormay be a movable point, such as successive teeth. The coupling meansemployed are preferably of such nature that the resistance and reactionare subject to regulation.

Simple and efiective forms of apparatus suitable for carrying on themethod of this invention are described by reference to the drawings,wherein Fig. 1 is a side view, with portions broken away, of one form ofapparatus suitable for carrying on the method of this invention;

Fig. 2 is a sectional view taken on the plane 2-2 of Fig. 1; and

Fig. 3 is a detail section of a tooth taken at .the line 3-3 of Fig. 2.

One form of apparatus suitable for carrying on the method of thisinvention is shown in Figs.

1 and 2 and consists of two pinions, a resisting or opposing pinion I,having a face width narrower than the face of the gear to be treated anda reacting pinion 2, which pinions are mounted to rotate in synchronism.Synchrom'sm is obtained by carrying pinion I upon shaft 3, which, asshown clearly in Fig. 2, is mounted to rotate in bearings 4, 5, and 6.The shaft 3 is rigidly keyedby key 1 to a pinion 8. The bearings 4, 5,and 6 are rigidly attached to a beam 9, which is mounted on bearings I0and II, which in turn are carried by a stationary gudgeon shaft I2. Agear I3 mounted on bearings I4 and I5 meshes with pinion 8 and rotatesabout the center of gudgeon shaft I2 so that pinion 8 remains inconstant mesh with gear I3, regardless of the position of beam 9. As asupport for the machine and as means for carrying the stationarygudgeon.

v same diameter as pinion 8 and the opposing and reacting pinions I and2 are of the same diameter and bear the same number of teeth. In thisway, as long as beam 9 is substantially stationary, resistor and reactorpinions I and 2 must remain synchronized.

. As shown clearly in Fig. 2, the shaft 3 carries as an integral partthereof a wide collar 20, into which collar studs 2I are secured. PinionI is provided with a series of slotted holes 22 that the angularrelation between the teeth of pinions I and 2 may be adjusted to anyposition desired by the use of clamping nuts 23. Th pinion 2 is securedin similar fashion to the shaft I8 so that replacement of pinions I and2 with others of different tooth form or pitch may be made. Tofacilitate this change, the beam 9 is provided with a removable portion24, held in position by means of bolts 25. The bed I6 is likewiseprovided with a removable portion 26 which is held in place by'means ofbolts 21.

Extending to the right of the gudgeon shaft I2 is a portion of the bedI6 which serves as a support for the loading mechanism. The loadingmechanism comprises standards 28 and 29 upon Whichthe fixed fulcrums 30and 3| are supported. A graduated beam 32 rests upon fulcrum 3| andthrough weights 33 and 34 loads the linkage 35 to any definite degreedesired. The linkage 35, through pivot 36, loads the lever 31, which inturn is supported on its pivot 38 on the fulcrum 30. Secured to thelever 31 is a counterweight I24, which is properly proportioned andpositioned to counterbalance the levers 31 and 32. The lever 31 beingloaded a definite, known amount loads the connecting member 39 andexerts a known load upon the pivot 40, which is an integral part, of thebeam 9. The beam 9 is also counterweighted to offset the heavy weight ofthe pinions at the working end of the machine. This is accomplished byhanging a properly adjusted weight I25 on the end of the beam 9.

The bed I6 carries a dove-tailed foot M which is fitted to slide in aguideway 42. The bed I6 is also drilled and adapted to threadinglyreceive the screw 43, which is rotatably mounted in a projection ofguide 42, not shown, so that the screw will rotate therein withoutlongitudinal movement and traverse the bed I6. Guide 42 is also providedwith a dove-tail foot 44 which is fitted to slide in a guideway 45 inthe foundation 46. The guideway 42 is drilled and adapted to threadinglyreceive a screw 41, which is mounted in a projection of the foundation46 to rotate therein without longitudinal movement and traverse theguideway 42 at right angles to the movement of bed I6. Screws 43 and 41are provided with means for turning the same, for example, as shown inthe hand-wheel 4B, which is attached to screw 41.

Means, not shown, are provided for mounting for rotation a gear to betreated, designated 49. Said gear is mounted in such position thatthrough the manipulation of screws 43 and 41 pinions I and 2 may bebrought into mesh with the gear 49. This operation is facilitated bylocking beam 9 against movement with respect to bed I6, loosening nuts23 and removing all back-lash by adjusting pinion l in the slotted holes22 and then clamping the nuts 23. In order to indicate the movements ofbeam 9 after adjustment of the pinions I and 2 to gear 49, any point ofreference in the loading system may be observed. A convenient Way ofaccomplishing this is by means of an ordinary extensometer gauge 50which is rigidly attached to the support of the loadin system. Thefeeler 5| of the gauge bears upon the lever 31. It may also beconvenient to atmen an extensometer gauge to the studs I23, shown inFig. 1. While it is useful to thus measuremovement of the parts, themethod of this invention is in no way dependent thereon.

It will be observed that the width of pinions I and 2 is narrow ascompared with the tooth face of the gear 49 and, further, as indicatedin Figs. 2 and 3, the teeth of pinions I and 2 are relieved or cut awayso that a bearing or contacting area 53 bears upon the teeth of gear 49.In this way, without excessive loading of the beam 9, very largestresses per unit length of tooth contact may be obtained. The stressesapplied to the gear being treated are thus localized in a small Zone andthe stress is applied in the form ofa rubbing, or combined rubbing androlling, action cross-wise of the tooth face being treated. The beam 32projects through a controlling standard I26, which is provided withadjusting screws I21 and I28. The latter may very conveniently beemployed as motion-limiting means during the operation of selectivelapping.

with the beam 32 to dampen the movement thereof. The dashpot ispreferably adjustable to any degree of dampening desired so thatappropriate dampening may be had for anydegree of loading. The link 39is also advantageously provided with a turn-buckle or right hand-lefthand coupling I3I so that deflections of the various parts may becompensated for.

In operating the device above described, it is convenient to place asmall block of rigid material in the nip 52 between the beam 9 and thebed I6 and to place sufficient weights 33 and 34 upon the loading systemto hold the beam relatively stationary with respect to the bed. Theproper pinions I and 2 for the gear 49 to be treated, which may be anyform of gear, helical or spur, involute or cycloidal, etc., are thenselected and put into place, as described above. By means of thehandwheel 48, the pinions I and 2 are brought into mesh with the gear 49and all back-lash removed at the slotted holes 22, as previouslydescribed. The weights 33 and 34 are then reduced so that the block inthe nip 52 can be removed. The screw 43 is then manipulated to positionthe pinions I and 2 at either one side or the other of the broad toothface of gear 49.

The smoothness with which the apparatus functions can be enhanced by theaddition of a dashpot I29, the latter being connected at/I30 With thegear to be treated thus prepared, the method of this invention may beemployed for either lapping or burnishing.

Lapping is accomplished by the method of this invention as, forinstance, in the above-described machine, by inserting a gauge block inthe nip 52, placing a moderate load upon the beam 32, and then rotatinggear 49 while applying a fine abrasive compound thereto while the gear49 is rotating the screw 43 is manipulated so that the contact area 53is applied over the entire face of gear 49. The gauge'block is sodimensioned that it supports all of the load placed on beam 32 when thegears I and 2 are in mesh with a theoretically perfect gear 49. theteeth of said gears I and 2 will approach gear 49 to contact therewith,but without the imposition of any load thereon. If, however, gear 49 isnot perfect, protrusions beyond the prescribed contour will force thegears I and 2 apart and open the nip 52 to an extent proportional to theprotrusion and, what is more important, transfer the load upon beam 32to the gear 49. The transfer of the load from the gauge block to thegear 49, whenever a protrusion occurs, and the return of the same to thegauge block whenever the gear lies within the prescribed contour,provides a selective means for causing the abrasive between the gear 49and the gears I and 2 to become active only against protruding parts. Inthis way a gear 49 having slight imperfections may be quite quickly andeasily corrected without the usual objectionable general reduction ofsub-contour, as well as protruding areas, which occurs to an appreciableextent in the old form of lapping. It will be seen that selectivelapping provides a means for the final correction of minute dimensionalerrors which heretofore could not be corrected.

Burnishing is accomplished by the method of this invention by simplymaking the loading of weights 33 and 34 sufficient so that africtionreducing finish will be produced on the teeth of gear 49 whenthe latter is rotated for a moderate length of time in contact withpinions I and 2, which at the same time are moved transversely acrossthe face of the gear 49. The gauge block is, of course, removed duringeither burnishing or lapping ifa selective effect is to be avoided.

In other words,

Bumishing as performed by this method of this invention is thus broughtabout by high local stressing of successive parts only of the length ofthe teeth of the gear being treated. In this way the method of thisinvention permits the use of moving contact stresses of sufficientintensity to cause surface metal in the gear to flow out into a verythin, highly polished layer, suchas is normally developed after longperiods use under load. In spite of the high unit stress employed by themethod of this invention and the rapidity with which the burnishedsurface is developed, the total loads placed upon the gear being treatedare moderate and the method may be carried on without danger of damageto the gear;

The employment of pinions narrower than the face of the gear to betreated makes possible high unit stresses for finishing purposes withoutthe necessity for building a very massive machine. The limited zone ofcontact is also useful in avoiding dangerous deflections of wide extentin a narrow central working area is useful in avoiding excessivestresses in the contacting pinions, but this is not essential.

Herein in the specification and claim the term "finishing" is used tomean the mechanical treatment of tooth surfaces, as by lapping orburnishing, to reduce the tool marks and scratches thereon and to bringabout a friction-reducing smoothness.

While instances of the application of the meth-- 0d of this inventionhave been illustrated, it is intended that the scope of Letters Patentgranted hereunder be not unnecessarily limited thereby, but that saidprotection extend to the full scope of the invention as represented bythe claim hereto appended.

What I claim as my invention is: The method of finishing gear teethsurfaces which consists in meshing with the teeth of a work gear to befinished a tool gear having an effective face narrower than the face ofsaid work gear, maintaining the shaft spacing between said work gear andsaid tool gear constant, causing the teeth of said tool gear to engagethe teeth of said work gear in a driving relationship to establish afinishing pressure between the engaging teeth of said work gear and saidtool gear while applying an opposite and tangential torque substantiallyequal to the torque resulting from said finishing pressure to. said workgear at a point on said work gear spaced from the zone of meshingengagement of said tool gear and work gear, and while said finishingpressure and said countertorque is maintained causing said work gear andtool gear to rotate in mesh withone another and to move axially with re-

